Low concentrations of Rhodamine-6G selectively destroy tumor cells and improve survival of melanoma transplanted mice

Abstract

Rhodamine-6G is a fluorescent dye binding to mitochondria, thus reducing the intact mitochondria number and inhibiting mitochondrial metabolic activity. Resultantly, the respiratory chain functioning becomes blocked, the cell "suffocated" and eventually destroyed. Unlike normal cells, malignant cells demonstrate a priori reduced mitochondrial numbers and aberrant metabolism. Therefore, a turning point might exist, when Rhodamine-induced loss of active mitochondria would selectively destroy malignant, but spare normal cells. Various malignant vs. non-malignant cell lines were cultured with Rhodamine-6G at different concentrations. In addition, C57Bl mice were implanted with B16-F10 melanoma and treated with Rhodamine-6G at different dosage/time regimens. Viability and proliferation of cultured tumor cells were time and dose-dependently inhibited, up to 90%, by Rhodamine-6G, with profound histological signs of cell death. By contrast, inhibition of normal control cell proliferation hardly exceeded 15-17%. Melanoma-transplanted mice receiving Rhodamine-6G demonstrated prolonged survival, improved clinical parameters, inhibited tumor growth and metastases count, compared to their untreated counterparts. Twice-a-week 10 -6 M Rhodamine-6G regimen yielded the most prominent results. We conclude that malignant, but not normal, cells are selectively destroyed by low doses of Rhodamine-6G. In vivo, such treatment selectively suppresses tumor progression and dissemination, thus improving prognosis. We suggest that selective anti-tumor properties of Rhodamine-6G are based on unique physiologic differences in energy metabolism between malignant and normal cells. If found clinically relevant, low concentrations of Rhodamine-6G might be useful for replacing, or backing up, more aggressive nonselective chemotherapeutic compounds. Key words: warburg effect, tumor, cell culture, melanoma, rhodamine-6G, mitochondriaCancer cells are unique in their energy turnover. Unlike normal tissues that derive most of their energy by metabolizing the consumed sugar to carbon dioxide and water (the process taking place within mitochondria), tumors obtain as much as half of their ATP by metabolizing glucose directly to lactic acid. Normal tissues use the process of oxidative phosphorylation within mitochondria for 90% of ATP production, and only 10% is produced by glucose consumption. By contrast, in tumor cells this ratio is 50%:50% [1][2][3]. This unique pattern of tumor metabolism has been described in early thirties of the past century and has been recognized since then as Warburg effect [1][2][3]. Recent studies employing molecular biology and proteomic imaging technologies, explained the basics of Warburg effect [4,5].Rhodamine-6G is a fluorescent dye capable of penetrating a living cell [6]. Upon entering the cell, Rhodamine-6G binds to the inner membranes of mitochondria. Based on these observations, it has been proposed that Rhodamine dyes may be used for producing fluorescent images of mitochondria with low background noise and high re...

Synergic Thermo- and pH-Sensitive Hybrid Microgels Loaded with Fluorescent Dyes and Ultrasmall Gold Nanoparticles for Photoacoustic Imaging and Photothermal Therapy

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Discrimination of Normal and Cancerous Human Skin Tissues Based on Laser-Induced Spectral Shift Fluorescence Microscopy

“…In other words, melanoma undergoes rapid cell growth while the uorophores are attached to ample mitochondria, damaging the entire cells. Note that the malignant cells are selectively demolished at low Rd6G doses, whereas the healthy ones may notably survive 52 .…”

Discrimination of normal and cancerous human skin tissues based on laser-induced spectral shift fluorescence microscopy

“…In other words, melanoma undergoes rapid cell growth while the fluorophores are attached to ample mitochondria, damaging the entire cells. Note that the malignant cells are selectively demolished at low Rd6G doses, whereas the healthy ones may notably survive 56 .…”